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How to read chlorine test strip results - Guide

How to Read Chlorine Test Strips


Chlorine test strips can quickly tell you how much chlorine is in a sample of water, but sometimes, understanding these seemingly simple results can be tricky.

How to interpret chlorine test strip results:

0 PPM: Not optimal
Water with 0 PPM free chlorine will not be disinfected if new bacteria are introduced.
0.5 PPM: Optimal
A free chlorine level of 0.5 PPM ensures water will remain bacteria free, even if new bacteria are introduced.
1 PPM: Good
Ensures water will remain bacteria free, even if new bacteria are introduced.
2 PPM: Not optimal
Once there is 2 PPM free chlorine present in water, it starts to have an unpleasant taste and odor.
While chlorine in water isn’t considered dangerous until it reaches above 4 PPM, water with 2 PPM chlorine tastes and smells like chemicals. Further testing would be required to determine if chlorine content is above the 4 PPM threshold. Test your water

To better understand what test strip results mean, let’s take a look at two types of chlorine testing often included on a chlorine test strip: Total Chlorine and Free Chlorine.

Difference between Total Chlorine and Free Chlorine

Most water treatment plants utilize chlorination, which involves adding chlorine to drinking water, as part of their disinfection process. When added in the right amounts, chlorine can effectively kill bacteria and prevent against future down-stream contamination.

During chlorination, chlorine is added to water and reacts with inorganic and organic materials to deactivate bacteria and kill microorganisms. The leftover chlorine that is not used to meet the chlorine demand is called total chlorine

Total chlorine is made up of: 

  1. Free Chlorine: leftover chlorine that is ready to deactivate bacteria
  2. Combined Chlorine: chlorine that has reacted with inorganic or organic molecules that can no longer deactivate bacteria. Your combined chlorine might include chloramine or disinfection byproducts called trihalomethanes.

Several trihalomethanes are carcinogenic. To know if your levels are higher than recommended drinking water standards you can test your water for total trihalomethanes in a certified lab. Test your water: Advanced City Water Test

What do chlorine test strips measure?

Most chlorine test strips measure either free chlorine or both free chlorine and total chlorine. The amount of free chlorine present tells you whether or not the water is safe to drink.

Tap Score City Water Tests measure both. 


How to interpret Chlorine Testing Strip Directions Tap Score

What is a safe amount of chlorine in drinking water?

The optimal concentration of chlorine residual is between 0.3 PPM and 0.5 PPM.

Levels from 0.2 PPM- 4 PPM are considered acceptable.

What does PPM stand for on chlorine strips?

PPM means parts per million. This measurement is the mass of a chemical or contaminate per unit volume of water. PPM or mg/L (milligrams per liter) is the same thing.

What is a dangerous amount of chlorine in drinking water?

The EPA states that ingesting water with chlorine levels above 4 PPM can cause negative health impacts.

How do I use my Tap Score chlorine testing strips?

Dip your strip into a glass of water (not your sampling container!) and move it back and forth for 30 seconds. Alternatively you can hold it under a stream of water for 10 seconds.

The pads will change color to indicate Total Chlorine (white pad on end) and Free Chlorine (yellow pad).

Chlorine Testing Strip Tap Score

Hold your strip up to the chart to see your result. Estimate results fall between two color blocks.

Compare your result to the chart

Need more Chlorine Testing Strips?

Note: All Tap Score City Water Tests include chlorine testing strips.

Why do we test chlorine with testing strips instead of sending it to the lab?

Although most contaminants are best tested with high accuracy at a certified laboratory, chlorine is a rare exception to this rule. Chlorine is a volatile substance that can dissipate over time so sending a water sample to the lab may not accurately reflect the chlorine levels at the point of use.

However, chlorine-related contamination, like disinfection byproducts can only be tested at a lab.

Test for disinfection byproducts


Why Trust Tap Score?

We know how confusing it can be to find advice on water quality and treatment you can trust. That’s part of the reason we made Tap Score—to help improve the way you test and treat your drinking water.

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  • Independent laboratory testing: Tap Score test results come from SimpleLab's third-party network of certified laboratories; in other words, accredited labs provide the data without conflicts of interest.
  • Continuously updated: Science never rests. That’s why our content always reflects the latest developments in scientific research and regulatory standards.
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About The Author


Kate leads operational strategy as COO at Tap Score and SimpleLab. She oversees daily, as well as long-term logistics for tens of thousands of environmental samples across hundreds of certified laboratories. However, she started her environmental testing career by way of scientific blog writing at Tap Score and it continues to be one of her favorite aspects of the business. Outside of Tap Score, Kate loves making homemade pasta, floral arranging, and singing along to Dolly Parton tunes.
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